You're protecting multiple servers from hackers, annoying people in chat, and many more inconveniences.
It's not a hobby.
Okay, that explanation was stupid. Lemme try again.
It doesn't really fit under volunteer, but I feel that it's a bit different than a hobby, because you can be demoted and literally be unable to do that hobby. With most hobies, you can just drop out of it when you wish, and while this applies here, you can be completely stopped from doing it altogether, and if you drop out of this one you can't pick it back up at any time. And yes, you can be completely stopped from doing a hobby if you like surfing and all of a sudden the oceans disappear, or some event that only you and a few other people know about with something really unique that you like to do gets cancelled or something, but that's rare.
So while it isn't volunteer work, I don't think it 100% fits under the definition of a hobby.